Once you start using birth control pills, your periods will be regulated by the hormones in the pills. This can cause your periods to change. Birth control pills can cause bleeding between periods, and your periods are likely to be lighter or you may not have periods at all. It is very important to take your pills at the same time every day.
The changes caused by the use of progesterone (such as Depo-Provera, Implanon, or mini-pills) are different for every woman. You may have normal periods, bleeding between periods, irregular bleeding, or no periods at all.
When you start using a new hormonal birth control method, ask your health professional what you can expect your periods to be like. If your pattern is very different from what you were expecting or if there is a sudden change in the timing or severity of bleeding, contact your health professional.
WebMD Medical Reference from Healthwise